( function () {
const _v1 = new THREE.Vector3();

const _v2 = new THREE.Vector3();

class VertexTangentsHelper extends THREE.LineSegments {
  constructor(object, size = 1, color = 0x00ffff) {
    const objGeometry = object.geometry;

    if (!(objGeometry && objGeometry.isBufferGeometry)) {
      console.error('THREE.VertexTangentsHelper: geometry not an instance of THREE.BufferGeometry.', objGeometry);
      return;
    }

    const nTangents = objGeometry.attributes.tangent.count; //

    const geometry = new THREE.BufferGeometry();
    const positions = new THREE.Float32BufferAttribute(nTangents * 2 * 3, 3);
    geometry.setAttribute('position', positions);
    super(geometry, new THREE.LineBasicMaterial({
      color,
      toneMapped: false
    }));
    this.object = object;
    this.size = size;
    this.type = 'VertexTangentsHelper'; //

    this.matrixAutoUpdate = false;
    this.update();
  }

  update() {
    this.object.updateMatrixWorld(true);
    const matrixWorld = this.object.matrixWorld;
    const position = this.geometry.attributes.position; //

    const objGeometry = this.object.geometry;
    const objPos = objGeometry.attributes.position;
    const objTan = objGeometry.attributes.tangent;
    let idx = 0; // for simplicity, ignore index and drawcalls, and render every tangent

    for (let j = 0, jl = objPos.count; j < jl; j++) {
      _v1.set(objPos.getX(j), objPos.getY(j), objPos.getZ(j)).applyMatrix4(matrixWorld);

      _v2.set(objTan.getX(j), objTan.getY(j), objTan.getZ(j));

      _v2.transformDirection(matrixWorld).multiplyScalar(this.size).add(_v1);

      position.setXYZ(idx, _v1.x, _v1.y, _v1.z);
      idx = idx + 1;
      position.setXYZ(idx, _v2.x, _v2.y, _v2.z);
      idx = idx + 1;
    }

    position.needsUpdate = true;
  }

}

THREE.VertexTangentsHelper = VertexTangentsHelper;
} )();
